Process for preparing a polymer dispersion and a polymer dispersion

ABSTRACT

The present invention relates to a process for preparing a polymer dispersion comprising polymerising one or more water soluble anionic monomers (m 1 ) and one or more non-ionic vinyl monomers (m 2 ) present in a reaction mixture further comprising a polymeric stabiliser (B) and a polymeric co-stabiliser (C). It further relates to a polymer dispersion, the use of the polymer dispersion and a process for producing paper.

This application is a continuation of patent application Ser. No.11/437,044 filed on May 19, 2006, which claims priority based on U.S.Provisional Patent Application No. 60/683,248, filed May 20, 2005, theentire contents of both are incorporated herein by reference.

The present invention relates to a process for preparing a polymerdispersion. It also relates to a polymer dispersion, the use of thepolymer dispersion and a process for producing paper.

BACKGROUND OF THE INVENTION

An important use of aqueous dispersions of anionic charged polymers isretention and dewatering aid in paper manufacturing industry. Furtheruses of such polymer dispersions are as aids in various processes wherethey act as, for example, flocculants when treating wastewater or aidsin other solid-liquid separation processes in, for example, the metal,ceramic, printing, biotechnological, and pharmaceutical industries. Theycan also be used as thickeners in, e.g., chemical, biotechnological,pharmaceutical, and cosmetic industries and soil improving agents.Generally, these polymer dispersions comprise a dispersed polymer and adispersant in which the dispersant usually is a polymeric dispersant.

Anionic polymer dispersions are generally prepared by polymerising areaction mixture of water-soluble anionic and non-ionic monomers in thepresence of a salt. Finished polymer will precipitate from the aqueoussalt solution and, by using a suitable dispersant, form a stable polymerdispersion. WO 01/18063, U.S. Pat. Nos. 5,837,776 and 5,605,970 discloseprocesses for preparing a dispersion of a water-soluble polymercomprising polymerising water-soluble monomers in an aqueous reactionmixture containing a salt.

Factors to consider are, for example, the process viscosity, activecontent, stability, good retention properties, and easiness of preparingthe polymer dispersion sometimes including preparing the stabiliser.Also, criteria such as environmental and safety aspects are ofimportance.

There are a number of criteria that the polymer dispersion should fulfilto give good results in the final application and be of commercialinterest. Such criteria are for example low-cost production, rapidperformance, effective flocculation or dewatering, and long shelf life.

Prior art anionic polymer dispersions described contain significantamounts of salt which makes up a great part of the weight of the polymerdispersion. There is presently a desire to reduce, or completely avoid,the use of salt in polymer dispersions due to environmental andeconomical reasons.

The viscosity of the reaction mixture when producing the polymerdispersion, “the process viscosity”, should be kept low and viscositypeaks should be avoided, or at least reduced as much as possible, duringthe production of the polymer dispersion.

The shelf life of the dispersion, i.e., the stability of the polymerdispersion over time, is an important property. An efficient dispersantis needed for keeping the polymer particles stable in dispersion withoutsettling as sediment.

A further factor to consider is the active content, i.e., the amount ofdispersed polymer in the polymer dispersion. A high active contentminimises transportation costs and gives easier handling at theend-application. By using an efficient dispersant, dispersions with ahigh active content can be obtained at the same time the viscosity canbe kept low. However, an increase of the active content above a certainlevel may not always give improved performance in retention anddewatering in a papermaking process.

During preparation of a polymer dispersion, deposits of polymer may formand stick to the reaction vessel and stirrer. This leads to timeconsuming cleaning procedures of the reaction equipment.

It is an object of the present invention to provide a, preferablysalt-free, water soluble anionic polymer dispersion having highstability and high active content. The polymer dispersion should alsogive good retention and dewatering results when used in papermakingprocesses, act as a good flocculant in other processes such as wastewater treatment, act as a good thickener in various applications such ascosmetic formulations and also be possible to use in soil improvementprocesses. It is further an object of the present invention to provide aprocess for preparing a, preferably salt-free, water soluble anionicpolymer dispersion in which the process viscosity is kept low and smoothduring preparation without any large viscosity peaks, and which gives nodeposits. Finally, it is an object of the present invention to provide aprocess for producing paper in which the polymer dispersion is used.

The Invention

By “stabiliser” is herein meant a polymer which function is to keepdispersed polymer particles/droplets in dispersion.

By “co-stabiliser” is herein meant a polymer which function is to make apolymer formed from polymerisation of one or more monomers toprecipitate out from solution into solid particles or liquid droplets.

According to the invention it has surprisingly been found that a highlystable polymer dispersion having high active content of a dispersedpolymer and low process viscosity can be achieved by a process forpreparing a polymer dispersion comprising polymerising one or moreanionic monomers (m₁) and one or more non-ionic vinyl monomers (m₂)present in a reaction mixture further comprising a polymeric stabiliser(B) and a polymeric co-stabilisers (C).

The invention further comprises a polymer dispersion comprising adispersed polymer (A) of one or more anionic monomers (m₁) and one ormore non-ionic vinyl monomers (m₂), a polymeric stabiliser (B), and apolymeric co-stabiliser (C).

The reaction medium is suitably an aqueous medium. The polymerdispersion is suitably an aqueous polymer dispersion. The polymerdispersion is suitably water-soluble. The polymer particles/dropletssuitably has an average size (thickness) of up to about 25 μm, alsosuitably from about 0.01 to about 25 μm, preferably from about 0.05 toabout 15 μm, most preferably from about 0.2 to about 10 μm.

The polymeric stabiliser (B) is suitably an organic polymer. Preferablythe polymeric stabiliser (B) is a polymer of one or more monomersbelonging to the group of acrylic acid, methacrylic acid, itaconic acid,2-acrylamido-2-methyl-1-propane sulphonic acid (AMPS),2-acrylamido-2-methyl-1-butane sulphonic acid (AMBS), acryloyloxyethylsulphonic acid, methacryloyloxyethyl sulphonic acid, acryloyloxypropylsulphonic acid, methacryloyloxypropyl sulphonic acid, vinyl sulphonicacid, allyl sulphonic acid, methallyl sulphonic acid, styrene sulphonicacid, maleic acid, maleamidic acid, and/or vinyl phosphonic acid. Othersuitable polymeric stabilizers are copolymers of maleic acid ormaleamidic acid, respectively, with styrene or vinyl ethers, oralpha-olefins which may contain additional comonomers. Preferably, thepolymeric stabiliser (B) is a copolymer of acrylic acid or methacrylicacid with a further of the listed monomers, preferably2-acrylamido-2-methyl-1-propane sulphonic acid (AMPS).

The weight average molecular weight of the polymeric stabiliser (B) issuitably from about 5,000 to about 5,000,000 g/mole, preferably fromabout 10,000 to about 1,000,000 g/mole, more preferably from about20,000 to about 1,000,000 g/mole, most preferably from about 35,000 toabout 500,000 g/mole.

The polymer dispersion suitably comprises from about 0.2 to about 5weight % of the polymeric stabiliser (B) based on the total weight ofthe dispersion or reaction mixture, preferably from about 0.5 to about 3weight %, most preferably from about 0.8 to about 1.5 weight %.

The polymeric co-stabiliser (C) is suitably an organic polymer.Preferably, the polymeric co-stabiliser (C) is a polymer of one or moremonomers belonging to the group of acrylic acid, methacrylic acid, vinylsulphonate, styrene sulphonic acid, itaconic acid, vinylphosphonic acid,2-acrylamido-2-methyl-1-propane sulphonic acid (AMPS),2-acrylamido-2-methyl-1-butane sulphonic acid (AMBS), acryloyloxyethylsulphonic acid, methacryloyloxyethyl sulphonic acid, acryloyloxypropylsulphonic acid, and methacryloyloxypropyl sulphonic acid.

Preferably, two or more co-stabilisers (C) are present in the reactionmixture and polymer dispersion.

The weight average molecular weight of the polymeric co-stabiliser (C)is suitably from about 100 to about 50,000 g/mol, preferably from about500 to about 30,000 g/mol, more preferably from about 1,000 to about20,000 g/mol, even more preferably from about 1,000 to about 15,000g/mol, most preferably from about 1,000 to about 10,000 g/mol.

The polymer dispersion suitably comprises from about 2 to about 50weight % of one or more polymeric co-stabilisers (C) based on the totalweight of the dispersion or reaction mixture, preferably from about 3 toabout 25 weight %, most preferably from about 5 to about 15 weight %.

The polymeric stabiliser (B) and the polymeric co-stabiliser (C) in thereaction mixture or polymer dispersion are preferably made up fromdifferent monomers or, if they are made up from the same monomers,contain different monomer ratios.

The polymeric stabiliser (B) or polymeric co-stabiliser (C) is suitablynot a dextrin or dextrin derivative.

The one or more anionic monomers (m₁) suitably belong to the group ofacrylic acid, methacrylic acid, (styrene sulphonic acid),2-acrylamido-2-methyl-1-propane sulphonic acid (AMPS),2-acrylamido-2-methyl-1-butane sulphonic acid (AMBS), acryloyloxyethylsulphonic acid, methacryloyloxyethyl sulphonic acid, acryloyloxypropylsulphonic acid, methacryloyloxypropyl sulphonic acid, vinyl sulphonicacid, and their alkali, earth alkali or ammonium salts.

The one or more non-ionic monomers (m₂) suitably belong to the group ofacrylamide, methacrylamide, N-methylacrylamide, N-methylmethacrylamide,N-ethylacrylamide, N-ethylmethacrylamide, N-isopropylacrylamide,N-isopropylmethacrylamide, N,N-dimethylacrylamide, N-t-butylacrylamide,N-t-butylmethacrylamide, N-hydroxyethylacrylamide,N-(tris-(hydroxymethyl)-methyl)-acrylamide, N-vinyl formamide, N-vinylacetamide, hydroxyalkylacrylate or hydroxyalkylmethacrylate with C2-C4alkyl, alkylacrylate or alkylmethacrylate with C1-C4 alkyl,benzylacrylate or benzylmethacrylate, esters of acrylic or methacrylicacid with dihydroxy-(polyethylene oxide) having 1-20 ethylene oxideunits, or esters of acrylic or methacrylic acid withmonomethoxyhydroxy-(polyethylene oxide) having 1-20 ethylene oxideunits. Preferably, the one or more non-ionic monomers (m₂) belong to thegroup of acrylamide, acrylate or methacrylate esters.

The molar ratio between the anionic monomer (m₁) and the non-ionicmonomer (m₂) is suitably from about 1:99 to about 25:75, preferably fromabout 3:97 to about 20:80, most preferably from about 5:95 to about15:85.

The weight average molecular weight of the dispersed polymer (A) issuitably from about 1,000,000 to about 15,000,000 g/mole, preferablyfrom about 1,500,000 to about 10,000,000 g/mole, most preferably fromabout 2,000,000 to about 8,000,000 g/mole.

The polymerisation is suitably a free-radical polymerisation. Theinitiator is suitably a radical former, preferably a water-solubleazo-initiator, a water-soluble peroxide, or a water-soluble redoxinitiator. Preferred initiators include 2,2′-azobis-(amidinpropane)hydrochloride, 2,2′-azobis-(2-methyl-N-(2-hydroxyethyl)-propionamide,4,4′-azobis-(4-cyanovaleric acid) and its alkali and ammonium salts,t-butylhydroperoxide, perhydrol, peroxydisulphate, or the beforementioned peroxides in combination with a reducing agent such as sodiummetabisulphite or ferrous salts.

The polymer dispersion suitably comprises from about 5 to about 40weight % of the dispersed polymer (A) based on the total weight of thedispersion, preferably from about 10 to about 30 weight %, mostpreferably from about 12 to about 25 weight %.

The amount of one or more inorganic salts in the polymer dispersion issuitably from 0 to about 1.9 weight % based on the total weight of thedispersion or reaction mixture, preferably from 0 to about 1 weight %,more preferably from 0 to about 0.5 weight %, most preferably from 0 toabout 0.1 weight %, or substantially salt-free.

By “inorganic salts” is herein suitably meant any inorganic salt,preferably salts belonging to the group of inorganic alkali metal,alkali earth metal or ammonium halides, sulphates and phosphates.

The polymer dispersion may also comprise additional substances, such ascross-linkers and branching agents.

The polymerisation temperature when may vary depending on, e.g., whichmonomers and polymerisation initiator are being used. Suitably, thepolymerisation temperature is from about 30 to about 90° C., preferablyfrom about 35 to about 70° C. The process is suitably a semi-batchprocess, i.e., the monomers m₁ and m₂ are both present at the beginningof the polymerisation process and further added at a later stage, eitherin one or more portions or continuously over a period of time during thereaction. The reaction mixture is suitably stirred during thepolymerisation process at a stirring rate suitable for the process.Suitably, the stirring rate is from about 100 to about 1000 rpm.

The invention further comprises use of a polymer dispersion as retentionand dewatering aid for paper manufacturing, as thickening agent, as soilimprovement agent and/or as an additive for increasing the dry strengthof paper. The polymer dispersion of the present invention can morespecifically be used as aid in various processes as, for example,flocculants when treating wastewater or aids in other solid-liquidseparation processes in, for example, the metal, ceramic, printing,biotechnological, and pharmaceutical industries. The polymer dispersioncan also be used as thickener in, e.g., chemical, biotechnological,pharmaceutical, and cosmetic industries.

Finally, the present invention comprises a process for the production ofpaper from an aqueous suspension containing cellulosic fibres, andoptional fillers, which comprises adding to the suspension an aqueouspolymer dispersion according to the invention, forming and draining thesuspension on a wire.

When using the polymer dispersion, according to the invention, inpapermaking processes, the dispersion is added to the suspension ofcellulosic fibres, and optional fillers, to be dewatered in amountswhich can vary within wide limits depending on, inter alia, type andnumber of components, type of furnish, filler content, type of filler,point of addition, etc. The dispersed polymer is usually added in anamount of at least 0.001%, often at least 0.005% by weight, based on drysubstance in the stock to be dewatered, and the upper limit is usually3% and suitably 1.5% by weight. The polymer dispersion according to theinvention is suitably diluted before adding it to the cellulosicsuspension. Further additives which are conventional in papermaking canof course be used in combination with the polymer dispersion accordingto the invention, such as, for example, silica-based sols, dry strengthagents, wet strength agents, optical brightening agents, dyes, sizingagents like rosin-based sizing agents and cellulose-reactive sizingagents, e.g. alkyl and alkenyl ketene dimers, alkyl and alkenyl ketenemultimers, and succinic anhydrides, etc. The cellulosic suspension, orstock, can also contain mineral fillers of conventional types such as,for example, kaolin, china clay, titanium dioxide, gypsum, talc andnatural and synthetic calcium carbonates such as chalk, ground marbleand precipitated calcium carbonate. The term “paper”, as used herein,include not only paper and the production thereof, but also othercellulosic fibre-containing sheet or web-like products, such as forexample board and paperboard, and the production thereof. The processcan be used in the production of paper from different types ofsuspensions of cellulose-containing fibres and the suspensions shouldsuitably contain at least 25% by weight and preferably at least 50% byweight of such fibres, based on dry substance. The suspension can bebased on fibres from chemical pulp such as sulphate, sulphite andorganosolv pulps, mechanical pulp such as thermome-chanical pulp,chemo-thermomechanical pulp, refiner pulp and groundwood pulp, from bothhardwood and softwood, and can also be based on recycled fibres,optionally from de-inked pulps, and mixtures thereof.

The invention will now further be described in connection with thefollowing examples which, however, not should be interpreted as limitingthe scope of the invention.

EXAMPLES Example 1

A stabiliser made of methacrylic acid (MAA) and2-acrylamido-2-methyl-1-propane sulphonic acid (AMPS) in a mole ratio of80:20 was prepared: A mixture of 85 g ultra-pure water, 8.24 g AMPS(solid), 16.62 g MAA and 11.5 g NaOH (50%) was adjusted to pH 7 by meansof NaOH (50%). 0.02 g EDTA (solid) was given into the mixture. Furtherultra-pure water was added to reach a total mass of 127 g. This wasfilled into a double-wall 150 ml glass reactor with anchor stirrer,nitrogen inlet, reflux condenser and bottom valve. The mixture wasstirred with 150/min and purged with nitrogen. The reactor content washeated up to 45° C. 0.05 g V-50 (2,2′-Azobis-(2-amidinopropane)dihydrochloride) were added. After 60 min, temperature was increased upto 50° C. The mixture was polymerised over 72 h at 50° C. and 150/min.The stabiliser was purified and isolated by ultrafiltration andfreeze-drying. The weight average molecular weight was about 15.000g/mole.

Examples 2-7

A polymer dispersion was prepared by polymerising a monomer mixturecomprising acrylamide and acrylic acid in the presence of a polymericstabiliser and a polymeric co-stabiliser.

A mixture of 30 g water, 24.3 g co-stabiliser polyacrylic acid (45%,Sigma-Aldrich, Mw 1,200), 1.2 g stabiliser poly (MAA-co-AMPS) (80:20)copolymer (according to example 1, Mw 15,000), 28.1 g acrylamide (50 wt%), 1.07 g acrylic acid, 0.04 g sodium formiate, 0.03 g EDTA, and 1.17 gNaOH (50 wt %) was stirred and the pH was adjusted to 7. Water was addedup to 100 g and during 8 hours azo-initiator VA-044 (4%)(2,2′-azobis-(N,N′-dimethyleneisobutyramidine) dihydrochloride, Wako)was added (0.5 g in steps). The temperature was kept at 35° C. After 16hours, the stirring was stopped.

Five further polymer dispersions were prepared using the same procedureas described above but changing the ratio non-ionic monomer and anionicmonomer, using a second non-ionic monomer in the dispersed polymer, andalso using as co-stabiliser in some cases a combination of polyacrylicacid and polymethacrylic acid. As stabiliser 1.2 weight %poly-(MMA-co-AMPS) in a mole ratio of 80:20 was used. The activecontents (polymer content) in the stabiliser was around 15 weight %. 11weight % of co-stabiliser was used.

TABLE 1 Dispersion anionic monomer non-ionic monomer co-stabiliserstabiliser Example 2 AA (10 mol-%) AAm (90 mol-%) PAA (Mw 1,200)poly-(MMA-co-AMPS) (Mw 15,000) Example 3 AA (15 mole-%) AAm (85 mole-%)PAA (Mw 1,200) poly-(MMA-co-AMPS) (Mw 20,000) Example 4 AA (15 mole-%)AAm (85 mole-%) PAA (Mw 1,200) poly-(MMA-co-AMPS) PMAA (Mw 9,500) (Mw20,000) (1:1 ratio) Example 5 MMA (10 mole-%) AAm (80 mole-%) PAA (Mw1,200) poly-(MMA-co-AMPS) AA (10 mole-%) (Mw 20,000) Example 6 MMA (10mole-%) AAm (80 mole-%) PAA (Mw 1,200) poly-(MMA-co-AMPS) t-BuA (10mole-%) (Mw 20,000) Example 7 MMA (10 mole-%) AAm (80 mole-%) PAA (Mw1,200) poly-(MMA-co-AMPS) n-BuA (10 mole-%) PMAA (Mw 9,500) (Mw 20,000)(1:1 ratio) In Table 1, the following abbreviations are used: AAM =acrylamide AA = acrylic acid MMA = methylmethacrylate t-BuA = t-butylacrylate n-BuA = n-butyl acrylate PAA = polyacrylic acid PMAA =polymethacrylic acid

The process viscosity was low (lower than ˜2000 mPas) for alldispersions.

Example 8

The polymer dispersions prepared in Examples 2-4 were tested forretention and dewatering performance in papermaking processes by meansof a Dynamic Drainage Analyser (DDA) available from Akribi, Sweden. Thefurnish used was based on 60% by weight of bleached 80/20 birch-pinepulp and 40% by weight of calcium carbonate. The stock volume was 800ml, the pulp concentration 5 g/L and the conductivity 1.5 mS/cm. Thestock was stirred at a speed of 1500 rpm while the following was addedto the stock: an anionic trash catcher (0.5 kg/t), polymer dispersion(1.0 kg/t) and finally anionic inorganic particles (0.5 kg/t). Thetemperature was 22.5° C. A vacuum of 0.35 bar was used for the analysis.The retention time (s) and turbidity (NTU) was measured.

TABLE 2 Polymer dispersions and application tests Application testsPolymer Polymer load Retention time Turbidity dispersion (kg/t) (s)(NTU) Example 2 1.0 15.2 198 Example 3 1.0 14.6 220 Example 4 1.0 13.2214

It is concluded that the dispersions according to the invention functionwell in retention and dewatering aids.

Example 9

The shelf life, measured as sedimentation stability, was tested for thedispersions according to Examples 2-7. A 10 g sample of each dispersionwas centrifuged for 30 minutes at 3000 rpm. The amount of polymersediment was determined for each sample. No sample gave any polymersediment

Thus, it is concluded that polymer dispersions with long shelf life canbe obtained by the present invention, also at high active contents.

The invention claimed is:
 1. Water-soluble polymer dispersioncomprising: a dispersed polymer (A) of one or more water-soluble anionicmonomers (m₁) and one or more non-ionic vinyl monomers (m₂); a polymericstabiliser (B); and a polymeric co-stabiliser (C), wherein the polymericstabiliser (B) and the polymeric co-stabiliser (C) are made of differentmonomers; wherein the polymeric dispersion comprises an amount ofinorganic salt of from 0 to about 0.5 weight % based on the total weightof the dispersion, wherein the one or more water-soluble anionicmonomers (m₁) is selected from the group consisting of acrylic acid,methacrylic acid, (styrene sulphonic acid),2-acrylamido-2-methyl-1-propane sulphonic acid (AMPS),2-acrylamido-2-methyl-1-butane sulphonic acid (AMBS), acryloyloxyethylsulphonic acid, methacryloyloxyethyl sulphonic acid, acryloyloxypropylsulphonic acid, methacryloyloxypropyl sulphonic acid, vinyl sulphonicacid, and their alkali, earth alkali or ammonium salts, wherein the oneor more non-ionic monomers (m₂) is selected from the group consisting ofacrylamide, methacrylamide, N-methylacrylamide, N-methylmethacrylamide,N-ethylacrylamide, N-ethylmethacrylamide, N-isopropylacrylamide,N-isopropylmethacrylamide, N,N-dimethylacrylamide, N-t-butylacrylamide,N-t-butylmethacrylamide, N-hydroxyethylacrylamide,N-(tris-(hydroxymethyl)-methyl)-acrylamide, N-vinyl formamide, N-vinylacetamide, hydroxyalkylacrylate or hydroxyalkylmethacrylate with C2-C4alkyl, alkylacrylate or alkylmethacrylate with C1-C4 alkyl,benzylacrylate or benzylmethacrylate, esters of acrylic or methacrylicacid with dihydroxy-(polyethylene oxide) having 1-20 ethylene oxideunits, and esters of acrylic or methacrylic acid withmonomethoxyhydroxy-(polyethylene oxide) having 1-20 ethylene oxideunits; and wherein the dispersion is free from dextrin or dextrinderivative.
 2. Polymer dispersion according to claim 1, wherein thedispersion is an aqueous polymer dispersion.
 3. Polymer dispersionaccording to claim 1, wherein the dispersion contains polymer particlesor droplets which have an average size of up to 25 μm.
 4. Polymerdispersion according to claim 1, wherein two or more co-stabilisers (C)are present in the polymer dispersion.
 5. Polymer dispersion accordingto claim 1, wherein the polymeric stabilizer (B) has a weight averagemolecular weight of from about 5,000 to about 5,000,000 g/mole. 6.Polymer dispersion according to claim 1, wherein the one or moremonomers (m₂) are selected from the group consisting of acrylamide,acrylate esters and methacrylate esters.
 7. Polymer dispersion accordingto claims 1, wherein the dispersion comprises an amount of inorganicsalt of from 0 to about 0.1 weight % based on the total weight of thedispersion.
 8. Polymer dispersion according to claim 1, wherein thepolymeric stabiliser (B) is a polymer of one or more monomers selectedfrom the group consisting of acrylic acid, methacrylic acid, itaconicacid, 2-acrylamido-2-methyl-1-propane sulphonic acid (AMPS),2-acrylamido-2-methyl-1-butane sulphonic acid (AMBS), acryloyloxyethylsulphonic acid, methacryloyloxyethyl sulphonic acid, acryloyloxypropylsulphonic acid, methacryloyloxypropyl sulphonic acid, vinyl sulphonicacid, allyl sulphonic acid, methallyl sulphonic acid, styrene sulphonicacid, maleic acid, maleamidic acid, and vinyl phosphonic acid, or acopolymer of i) maleic acid or maleamidic acid, with ii) styrene, vinylethers or alpha-olefins.
 9. Polymer dispersion according to claim 1;wherein the polymeric co-stabiliser (C) is a polymer of one or moremonomers selected from the group consisting of acrylic acid, methacrylicacid, vinyl sulphonate, styrene sulphonic acid, itaconic acid,vinylphosphonic acid, 2-acrylamido-2-methyl-1-propane sulphonic acid(AMPS), 2-acrylamido-2-methyl-1-butane sulphonic acid (AMBS),acryloyloxyethyl sulphonic acid, methacryloyloxyethyl sulphonic acid,acryloyloxypropyl sulphonic acid, and methacryloyloxypropyl sulphonicacid.
 10. Polymer dispersion according to claim 1, wherein thedispersion comprises from about 10 to about 30 weight % of the dispersedpolymer (A); from about 0.5 to about 3 weight % of the polymericstabiliser (B); and from about 3 to about 25 weight % of the polymericco-stabiliser (C).
 11. Polymer dispersion according to claim 10, whereinthe dispersion comprises from about 0.8 to about 1.5 wt % of thepolymeric stabiliser (B) and from about 5 to about 15 wt % of thepolymeric co-stabiliser (C).
 12. Polymer dispersion according to claim1, wherein the weight average molecular weight of the polymericco-stabiliser (C) is from about 1,000 to about 20,000 g/mole. 13.Process for the production of paper from an aqueous suspensioncontaining cellulosic fibres, and optional fillers, which comprisesadding to the suspension a polymer dispersion according to claim 1,forming and draining the suspension on a wire.
 14. Aqueous water-solublepolymer dispersion comprising: a dispersed polymer (A) of one or morewater-soluble anionic monomers (m_(i)) and one or more non-ionic vinylmonomers (m₂) selected from the group consisting of acrylamide, acrylateesters and methacrylate esters; a polymeric stabiliser (B); and apolymeric co-stabiliser (C), wherein the polymeric dispersion comprisesan amount of inorganic salt of from 0 to about 0.1 weight % based on thetotal weight of the dispersion, and wherein the dispersion is free fromdextrin or dextrin derivative.
 15. Polymer dispersion according to claim14, wherein the polymeric stabiliser (B) is a polymer of one or moremonomers selected from the group consisting of acrylic acid, methacrylicacid, itaconic acid, 2-acrylamido-2-methyl-1-propane sulphonic acid(AMPS), 2-acrylamido-2-methyl-1-butane sulphonic acid (AMBS),acryloyloxyethyl sulphonic acid, methacryloyloxyethyl sulphonic acid,acryloyloxypropyl sulphonic acid, methacryloyloxypropyl sulphonic acid,vinyl sulphonic acid, allyl sulphonic acid, methallyl sulphonic acid,styrene sulphonic acid, maleic acid, maleamidic acid, and vinylphosphonic acid, or a copolymer of i) maleic acid or maleamidic acid,with ii) styrene, vinyl ethers or alpha-olefins.
 16. Polymer dispersionaccording to claim 14; wherein the polymeric co-stabiliser (C) is apolymer of one or more monomers selected from the group consisting ofacrylic acid, methacrylic acid, vinyl sulphonate, styrene sulphonicacid, itaconic acid, vinylphosphonic acid,2-acrylamido-2-methyl-1-propane sulphonic acid (AMPS),2-acrylamido-2-methyl-1-butane sulphonic acid (AMBS), acryloyloxyethylsulphonic acid, methacryloyloxyethyl sulphonic acid, acryloyloxypropylsulphonic acid, and methacryloyloxypropyl sulphonic acid.
 17. Polymerdispersion according to claim 14, wherein the dispersion comprises fromabout 10 to about 30 weight % of the dispersed polymer (A); from about0,5 to about 3 weight % of the polymeric stabiliser (B); and from about3 to about 25 weight % of the co-stabiliser (C).
 18. Polymer dispersionaccording to claim 14; wherein the dispersion comprises from about 0.8to about 1.5 wt % of the stabiliser (B) and from about 5 to 15 wt % ofthe polymeric co-stabiliser (C).